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<div class="title">samples/cpp/warpPerspective_demo.cpp</div>  </div>
</div><!--header-->
<div class="contents">
<p>An example program shows using <a class="el" href="../../da/d54/group__imgproc__transform.html#ga20f62aa3235d869c9956436c870893ae" title="Calculates a perspective transform from four pairs of the corresponding points. ">cv::getPerspectiveTransform</a> and <a class="el" href="../../da/d54/group__imgproc__transform.html#gaf73673a7e8e18ec6963e3774e6a94b87" title="Applies a perspective transformation to an image. ">cv::warpPerspective</a> for image warping</p>
<div class="fragment"><div class="line"></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d6/d87/imgcodecs_8hpp.html">opencv2/imgcodecs.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d8/dcc/namespacestd.html">std</a>;</div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> help(<span class="keywordtype">char</span>** argv)</div><div class="line">{</div><div class="line">    <span class="comment">// print a welcome message, and the OpenCV version</span></div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nThis is a demo program shows how perspective transformation applied on an image, \n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;Using OpenCV version &quot;</span> &lt;&lt; <a name="a0"></a><a class="code" href="../../da/dd7/core_2include_2opencv2_2core_2version_8hpp.html#a4f050efda432e041621b3af3df140adc">CV_VERSION</a> &lt;&lt; endl;</div><div class="line"></div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nUsage:\n&quot;</span> &lt;&lt; argv[0] &lt;&lt; <span class="stringliteral">&quot; [image_name -- Default right.jpg]\n&quot;</span> &lt;&lt; endl;</div><div class="line"></div><div class="line">    cout &lt;&lt; <span class="stringliteral">&quot;\nHot keys: \n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;\tESC, q - quit the program\n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;\tr - change order of points to rotate transformation\n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;\tc - delete selected points\n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;\ti - change order of points to inverse transformation \n&quot;</span></div><div class="line">         <span class="stringliteral">&quot;\nUse your mouse to select a point and move it to see transformation changes&quot;</span> &lt;&lt; endl;</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> onMouse(<span class="keywordtype">int</span> event, <span class="keywordtype">int</span> x, <span class="keywordtype">int</span> y, <span class="keywordtype">int</span>, <span class="keywordtype">void</span>*);</div><div class="line"><a name="_a1"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> warping(<a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> image, <a name="_a2"></a><a class="code" href="../../d6/d50/classcv_1_1Size__.html">Size</a> warped_image_size, vector&lt; Point2f&gt; srcPoints, vector&lt; Point2f&gt; dstPoints);</div><div class="line"></div><div class="line"><a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a> windowTitle = <span class="stringliteral">&quot;Perspective Transformation Demo&quot;</span>;</div><div class="line"><a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a> labels[4] = { <span class="stringliteral">&quot;TL&quot;</span>,<span class="stringliteral">&quot;TR&quot;</span>,<span class="stringliteral">&quot;BR&quot;</span>,<span class="stringliteral">&quot;BL&quot;</span> };</div><div class="line">vector&lt; Point2f&gt; roi_corners;</div><div class="line">vector&lt; Point2f&gt; midpoints(4);</div><div class="line">vector&lt; Point2f&gt; dst_corners(4);</div><div class="line"><span class="keywordtype">int</span> roiIndex = 0;</div><div class="line"><span class="keywordtype">bool</span> dragging;</div><div class="line"><span class="keywordtype">int</span> selected_corner_index = 0;</div><div class="line"><span class="keywordtype">bool</span> validation_needed = <span class="keyword">true</span>;</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main(<span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv)</div><div class="line">{</div><div class="line">    help(argv);</div><div class="line">    <a name="_a3"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">CommandLineParser</a> parser(argc, argv, <span class="stringliteral">&quot;{@input| right.jpg |}&quot;</span>);</div><div class="line"></div><div class="line">    <span class="keywordtype">string</span> filename = <a name="a4"></a><a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>(parser.<a name="a5"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html#a190215863579a6d244dccfd261ee0224">get</a>&lt;<span class="keywordtype">string</span>&gt;(<span class="stringliteral">&quot;@input&quot;</span>));</div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> original_image = <a name="a6"></a><a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( filename );</div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> image;</div><div class="line"></div><div class="line">    <span class="keywordtype">float</span> original_image_cols = (float)original_image.<a name="a7"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a>;</div><div class="line">    <span class="keywordtype">float</span> original_image_rows = (<span class="keywordtype">float</span>)original_image.<a name="a8"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>;</div><div class="line">    roi_corners.push_back(<a name="a9"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>( (<span class="keywordtype">float</span>)(original_image_cols / 1.70), (<span class="keywordtype">float</span>)(original_image_rows / 4.20) ));</div><div class="line">    roi_corners.push_back(<a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>( (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a> / 1.15), (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a> / 3.32) ));</div><div class="line">    roi_corners.push_back(<a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>( (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a> / 1.33), (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a> / 1.10) ));</div><div class="line">    roi_corners.push_back(<a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>( (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a> / 1.93), (<span class="keywordtype">float</span>)(original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a> / 1.36) ));</div><div class="line"></div><div class="line">    <a name="a10"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>(windowTitle, <a name="a11"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#ggabf7d2c5625bc59ac130287f925557ac3a29e45c5af696f73ce5e153601e5ca0f1">WINDOW_NORMAL</a>);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>(<span class="stringliteral">&quot;Warped Image&quot;</span>, <a name="a12"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#ggabf7d2c5625bc59ac130287f925557ac3acf621ace7a54954cbac01df27e47228f">WINDOW_AUTOSIZE</a>);</div><div class="line">    <a name="a13"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga8d86b207f7211250dbe6e28f76307ffb">moveWindow</a>(<span class="stringliteral">&quot;Warped Image&quot;</span>, 20, 20);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga8d86b207f7211250dbe6e28f76307ffb">moveWindow</a>(windowTitle, 330, 20);</div><div class="line"></div><div class="line">    <a name="a14"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga89e7806b0a616f6f1d502bd8c183ad3e">setMouseCallback</a>(windowTitle, onMouse, 0);</div><div class="line"></div><div class="line">    <span class="keywordtype">bool</span> endProgram = <span class="keyword">false</span>;</div><div class="line">    <span class="keywordflow">while</span> (!endProgram)</div><div class="line">    {</div><div class="line">        <span class="keywordflow">if</span> ( validation_needed &amp; (roi_corners.size() &lt; 4) )</div><div class="line">        {</div><div class="line">            validation_needed = <span class="keyword">false</span>;</div><div class="line">            image = original_image.<a name="a15"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#adff2ea98da45eae0833e73582dd4a660">clone</a>();</div><div class="line"></div><div class="line">            <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i &lt; roi_corners.size(); ++i)</div><div class="line">            {</div><div class="line">                <a name="a16"></a><a class="code" href="../../d9/db7/group__datasets__gr.html#gga610754124ced68d1f05760b5948fbb76a6f0d8b2d9e3e947b2a5c1eff9e81ee95">circle</a>( image, roi_corners[i], 5, <a name="a17"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 255, 0), 3 );</div><div class="line"></div><div class="line">                <span class="keywordflow">if</span>( i &gt; 0 )</div><div class="line">                {</div><div class="line">                    <a name="a18"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>(image, roi_corners[i-1], roi_corners[(i)], <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 0, 255), 2);</div><div class="line">                    <a class="code" href="../../d9/db7/group__datasets__gr.html#gga610754124ced68d1f05760b5948fbb76a6f0d8b2d9e3e947b2a5c1eff9e81ee95">circle</a>(image, roi_corners[i], 5, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 255, 0), 3);</div><div class="line">                    <a name="a19"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga5126f47f883d730f633d74f07456c576">putText</a>(image, labels[i].c_str(), roi_corners[i], <a name="a20"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#gga0f9314ea6e35f99bb23f29567fc16e11afff8b973668df2e4028dddc5274310c9">FONT_HERSHEY_SIMPLEX</a>, 0.8, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(255, 0, 0), 2);</div><div class="line">                }</div><div class="line">            }</div><div class="line">            <a name="a21"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( windowTitle, image );</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span> ( validation_needed &amp; ( roi_corners.size() == 4 ))</div><div class="line">        {</div><div class="line">            image = original_image.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#adff2ea98da45eae0833e73582dd4a660">clone</a>();</div><div class="line">            <span class="keywordflow">for</span> ( <span class="keywordtype">int</span> i = 0; i &lt; 4; ++i )</div><div class="line">            {</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>(image, roi_corners[i], roi_corners[(i + 1) % 4], <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 0, 255), 2);</div><div class="line">                <a class="code" href="../../d9/db7/group__datasets__gr.html#gga610754124ced68d1f05760b5948fbb76a6f0d8b2d9e3e947b2a5c1eff9e81ee95">circle</a>(image, roi_corners[i], 5, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 255, 0), 3);</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga5126f47f883d730f633d74f07456c576">putText</a>(image, labels[i].c_str(), roi_corners[i], <a class="code" href="../../d6/d6e/group__imgproc__draw.html#gga0f9314ea6e35f99bb23f29567fc16e11afff8b973668df2e4028dddc5274310c9">FONT_HERSHEY_SIMPLEX</a>, 0.8, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(255, 0, 0), 2);</div><div class="line">            }</div><div class="line"></div><div class="line">            <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( windowTitle, image );</div><div class="line"></div><div class="line">            midpoints[0] = (roi_corners[0] + roi_corners[1]) / 2;</div><div class="line">            midpoints[1] = (roi_corners[1] + roi_corners[2]) / 2;</div><div class="line">            midpoints[2] = (roi_corners[2] + roi_corners[3]) / 2;</div><div class="line">            midpoints[3] = (roi_corners[3] + roi_corners[0]) / 2;</div><div class="line"></div><div class="line">            dst_corners[0].x = 0;</div><div class="line">            dst_corners[0].y = 0;</div><div class="line">            dst_corners[1].x = (float)<a name="a22"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga4e556cb8ad35a643a1ea66e035711bb9">norm</a>(midpoints[1] - midpoints[3]);</div><div class="line">            dst_corners[1].y = 0;</div><div class="line">            dst_corners[2].x = dst_corners[1].x;</div><div class="line">            dst_corners[2].y = (float)<a class="code" href="../../dc/d84/group__core__basic.html#ga4e556cb8ad35a643a1ea66e035711bb9">norm</a>(midpoints[0] - midpoints[2]);</div><div class="line">            dst_corners[3].x = 0;</div><div class="line">            dst_corners[3].y = dst_corners[2].y;</div><div class="line"></div><div class="line">            <a class="code" href="../../d6/d50/classcv_1_1Size__.html">Size</a> warped_image_size = <a name="a23"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga346f563897249351a34549137c8532a0">Size</a>(<a name="a24"></a><a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(dst_corners[2].x), <a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(dst_corners[2].y));</div><div class="line"></div><div class="line">            <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> M = <a name="a25"></a><a class="code" href="../../da/d54/group__imgproc__transform.html#ga20f62aa3235d869c9956436c870893ae">getPerspectiveTransform</a>(roi_corners, dst_corners);</div><div class="line"></div><div class="line">            <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> warped_image;</div><div class="line">            <a name="a26"></a><a class="code" href="../../d5/df1/group__imgproc__hal__functions.html#ga843a5226c302e59fe09b08f424e08795">warpPerspective</a>(original_image, warped_image, M, warped_image_size); <span class="comment">// do perspective transformation</span></div><div class="line"></div><div class="line">            <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;Warped Image&quot;</span>, warped_image);</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordtype">char</span> c = (char)<a name="a27"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>( 10 );</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span> ((c == <span class="charliteral">&#39;q&#39;</span>) | (c == <span class="charliteral">&#39;Q&#39;</span>) | (c == 27))</div><div class="line">        {</div><div class="line">            endProgram = <span class="keyword">true</span>;</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span> ((c == <span class="charliteral">&#39;c&#39;</span>) | (c == <span class="charliteral">&#39;C&#39;</span>))</div><div class="line">        {</div><div class="line">            roi_corners.clear();</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span> ((c == <span class="charliteral">&#39;r&#39;</span>) | (c == <span class="charliteral">&#39;R&#39;</span>))</div><div class="line">        {</div><div class="line">            roi_corners.push_back(roi_corners[0]);</div><div class="line">            roi_corners.erase(roi_corners.begin());</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="keywordflow">if</span> ((c == <span class="charliteral">&#39;i&#39;</span>) | (c == <span class="charliteral">&#39;I&#39;</span>))</div><div class="line">        {</div><div class="line">            <a name="a28"></a><a class="code" href="../../d0/de1/group__core.html#gafbc8f513f40dc1b7c2d48ea6a5a81776">swap</a>(roi_corners[0], roi_corners[1]);</div><div class="line">            <a class="code" href="../../d0/de1/group__core.html#gafbc8f513f40dc1b7c2d48ea6a5a81776">swap</a>(roi_corners[2], roi_corners[3]);</div><div class="line">        }</div><div class="line">    }</div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">static</span> <span class="keywordtype">void</span> onMouse(<span class="keywordtype">int</span> event, <span class="keywordtype">int</span> x, <span class="keywordtype">int</span> y, <span class="keywordtype">int</span>, <span class="keywordtype">void</span>*)</div><div class="line">{</div><div class="line">    <span class="comment">// Action when left button is pressed</span></div><div class="line">    <span class="keywordflow">if</span> (roi_corners.size() == 4)</div><div class="line">    {</div><div class="line">        <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; 4; ++i)</div><div class="line">        {</div><div class="line">            <span class="keywordflow">if</span> ((event == <a name="a29"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#gga927593befdddc7e7013602bca9b079b0ad3419100fc2d7688c6dbe3da030fbfd9">EVENT_LBUTTONDOWN</a>) &amp; ((<a name="a30"></a><a class="code" href="../../d2/d75/namespacecv.html#af6df65b17fb11af6d34634b6dfa44683">abs</a>(roi_corners[i].x - x) &lt; 10)) &amp; (<a class="code" href="../../d2/d75/namespacecv.html#af6df65b17fb11af6d34634b6dfa44683">abs</a>(roi_corners[i].y - y) &lt; 10))</div><div class="line">            {</div><div class="line">                selected_corner_index = i;</div><div class="line">                dragging = <span class="keyword">true</span>;</div><div class="line">            }</div><div class="line">        }</div><div class="line">    }</div><div class="line">    <span class="keywordflow">else</span> <span class="keywordflow">if</span> ( event == <a class="code" href="../../d0/d90/group__highgui__window__flags.html#gga927593befdddc7e7013602bca9b079b0ad3419100fc2d7688c6dbe3da030fbfd9">EVENT_LBUTTONDOWN</a> )</div><div class="line">    {</div><div class="line">        roi_corners.push_back( <a class="code" href="../../dc/d84/group__core__basic.html#ga7d080aa40de011e4410bca63385ffe2a">Point2f</a>( (<span class="keywordtype">float</span>) x, (<span class="keywordtype">float</span>) y ) );</div><div class="line">        validation_needed = <span class="keyword">true</span>;</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Action when left button is released</span></div><div class="line">    <span class="keywordflow">if</span> (event == <a name="a31"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#gga927593befdddc7e7013602bca9b079b0a59cad7ffe959adf2782a110196d47bf6">EVENT_LBUTTONUP</a>)</div><div class="line">    {</div><div class="line">        dragging = <span class="keyword">false</span>;</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Action when left button is pressed and mouse has moved over the window</span></div><div class="line">    <span class="keywordflow">if</span> ((event == <a name="a32"></a><a class="code" href="../../d0/d90/group__highgui__window__flags.html#gga927593befdddc7e7013602bca9b079b0a8f2ec5fd35fe3f4b696518b146dcf675">EVENT_MOUSEMOVE</a>) &amp;&amp; dragging)</div><div class="line">    {</div><div class="line">        roi_corners[selected_corner_index].x = (float) x;</div><div class="line">        roi_corners[selected_corner_index].y = (float) y;</div><div class="line">        validation_needed = <span class="keyword">true</span>;</div><div class="line">    }</div><div class="line">}</div></div><!-- fragment --> </div><!-- contents -->
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